The telephony industry has long used certain standards in managing the processes which occur when land-line telephones are used to make out-going calls. Generally, when a telephone goes off-hook, a circuit is established between the telephone and a central office. The central office typically includes complex, sophisticated, and expensive equipment which provide the intelligence to manage the call origination process. The central office applies dial tone to the telephone's local loop as soon as the off-hook condition is detected. Dial tone provides audible feedback which informs the user that the system is waiting for the user's input. After a first digit is dialed, the central office removes the dial tone.
As the user continues to dial digits, the central office analyzes the digits in order to determine routing and call charges and to identify when an entire phone number has been dialed. This analysis is a complex task because a wide variety of call types may be originated at the telephone. For example, local calls, non-toll inter NPA calls, toll calls, operator assisted calls, international calls, and other types of calls must be distinguished from one another, and the different types of calls may require the dialing of different lengths of digit streams. In areas where central offices in different area codes or LATAs reside near one another, hundreds of central office codes must be distinguished from hundreds of other central office codes. Moreover, these complex rules for dialed number analysis differ from central office to central office so that each central office essentially implements its own unique number analysis plan.
Cellular telephony has adopted a slightly different technique for originating calls. Generally, a user manipulates a handset to store dialed digits in a digit buffer memory located at a cellular radiotelephone. When the user has entered a complete number in the digit buffer, the user presses a "send" key, which signals a conventional radiotelephone to send an origination message to the network. The network then analyzes the digits in a manner similar to that done for land-line telephones. This technique conserves the RF spectrum because the network does not allocate the scarce resource of an RF channel to the radiotelephone at the instant an off-hook condition occurs, but waits until after the user presses the send key.
On the other hand, the conventional cellular telephony call origination technique causes several problems. For example, this technique is different from the widely understood and ubiquitous land-line telephony call origination process. The difference causes numerous complications. New cellular customers must be taught a call origination process that is different from one with which they are usually familiar, and a large cost is associated with teaching a new process to an entire population of users. For many users, the use of a different call origination process causes confusion, which ultimately leads to dissatisfaction. No audible feedback, such as the well known dial tone, is provided to let users know that their instrument is awaiting user input, and many users who are accustomed to the land-line telephony call origination process often become distracted by the lack of this feedback. In addition, the cellular call origination process requires the extra step of pressing the send key. This extra step seems unnatural and is easily forgotten by new users who are accustomed to the land-line telephony call origination process.
Various prior art cellular telephony devices have attempted to make the cellular call origination process more closely resemble the corresponding land-line process. For example, a few prior art cellular devices have generated a dial tone at the radiotelephone itself to provide the familiar feedback. However, these devices have been encumbered by additional switches and related mechanisms that establish on-hook and off-hook conditions and that generally limit the devices' portability and flexibility.
In addition, various prior art cellular telephony devices have attempted to detect when a user completes the dialing activity so that the device may then automatically send an origination message to the cellular network without requiring a user to press a send key. These prior art cellular devices usually wait until no additional key presses are detected at a keypad for a predetermined duration before automatically sending the origination message to the network. Unfortunately, for this technique to be reliable the waiting duration needs to be around three to eight seconds, which is an undesirably long and annoying wait to impose upon users.
Still other devices have attempted to interface between land-line telephone devices and conventional cellular radiotelephones. Such devices have attempted to simulate the operation of a central office insofar as supplying conventional central-office signals to the land-line telephone devices and in evaluating land-line telephone touch tone/rotary dial type signals to determine when a last digit has been dialed. However, such devices are hard-wired or otherwise permanently programmed to simulate a particular's central office's local dialing plan, have only a limited ability to automatically detect the completion of dialing, and are intended only for stationary use at a location covered by the central office whose local dialing plan is being simulated.